Kyle,
First, congrats on the new lens.
I'm using the TC-17 with my 70-200 VR and they are nicely matched. The TC-17 is actually pretty sharp even at full resolution.
BTW you're maximum aperture is off.
1.4x with an F/2.8 lens is F/4
1.7x with an F/2.8 lens is F/4.8
2.0x with an F/2.8 lens is F/5.6
From what I've heard, the 2.0 imacts the autofocus speed noticably. I haven't had much issue with the 1.7x.
The 1.7x would be a pretty good compromise. You get the extra range of the 1.7x (340mm vs 280 for the 1.4x) and you also get a sharper converter than the 2.0.
When I have been shooting with the 1.7x I very occasionally wish I also had a 2.0 for that little bit of extra reach, but thus far I haven't found myself wanting for a 1.4x in addition to the 1.7x.
Hope that helps a little with your decision making process.
I'm looking forward to some photos from you soon from the new lens.
